Fluid handling structure including gas supply and gas recovery openings, lithographic apparatus and device manufacturing method

ABSTRACT

A fluid handling structure for a lithographic apparatus, the fluid handling structure having, at a boundary from a space configured to contain immersion fluid to a region external to the fluid handling structure: a meniscus pinning feature to resist passage of immersion fluid in a radially outward direction from the space; a plurality of gas supply openings in a linear array at least partly surrounding and radially outward of the meniscus pinning feature; and a gas recovery opening radially outward of the plurality of gas supply openings in a linear array.

This application claims priority and benefit under 35 U.S.C. §119(e) toU.S. Provisional Patent Application No. 61/506,442, filed on Jul. 11,2011 and to U.S. Provisional Patent Application No. 61/526,992, filed onAug. 24, 2011. The content of those applications are incorporated hereinin their entirety by reference.

FIELD

The present invention relates to a fluid handling structure, alithographic apparatus and a method for manufacturing a device using alithographic apparatus.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.comprising part of, one, or several dies) on a substrate (e.g. a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion at one time, andso-called scanners, in which each target portion is irradiated byscanning the pattern through a radiation beam in a given direction (the“scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible totransfer the pattern from the patterning device to the substrate byimprinting the pattern onto the substrate.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water, so as to fill a space between the final element ofthe projection system and the substrate. In an embodiment, the liquid isdistilled water, although another liquid can be used. An embodiment ofthe invention will be described with reference to liquid. However,another fluid may be suitable, particularly a wetting fluid, anincompressible fluid and/or a fluid with higher refractive index thanair, desirably a higher refractive index than water. Fluids excludinggases are particularly desirable. The point of this is to enable imagingof smaller features since the exposure radiation will have a shorterwavelength in the liquid. (The effect of the liquid may also be regardedas increasing the effective numerical aperture (NA) of the system andalso increasing the depth of focus.) Other immersion liquids have beenproposed, including water with solid particles (e.g. quartz) suspendedtherein, or a liquid with a nano-particle suspension (e.g. particleswith a maximum dimension of up to 10 nm). The suspended particles may ormay not have a similar or the same refractive index as the liquid inwhich they are suspended. Other liquids which may be suitable include ahydrocarbon, such as an aromatic, a fluorohydrocarbon, and/or an aqueoussolution.

Submersing the substrate or substrate and substrate table in a bath ofliquid (see, for example, U.S. Pat. No. 4,509,852) means that there is alarge body of liquid that must be accelerated during a scanningexposure. This requires additional or more powerful motors andturbulence in the liquid may lead to undesirable and unpredictableeffects.

In an immersion apparatus, immersion fluid is handled by a fluidhandling system, device structure or apparatus. In an embodiment thefluid handling system may supply immersion fluid and therefore be afluid supply system. In an embodiment the fluid handling system may atleast partly confine immersion fluid and thereby be a fluid confinementsystem. In an embodiment the fluid handling system may provide a barrierto immersion fluid and thereby be a barrier member, such as a fluidconfinement structure. In an embodiment the fluid handling system maycreate or use a flow of gas, for example to help in controlling the flowand/or the position of the immersion fluid. The flow of gas may form aseal to confine the immersion fluid so the fluid handling structure maybe referred to as a seal member; such a seal member may be a fluidconfinement structure. In an embodiment, immersion liquid is used as theimmersion fluid. In that case the fluid handling system may be a liquidhandling system. In reference to the aforementioned description,reference in this paragraph to a feature defined with respect to fluidmay be understood to include a feature defined with respect to liquid.

SUMMARY

If the immersion liquid is confined by a fluid handling system to alocalized area on the surface which is under the projection system, ameniscus extends between the fluid handling system and the surface. Ifthe meniscus collides with a droplet on the surface, this may result ininclusion of a bubble in the immersion liquid. The droplet may bepresent on the surface for various reasons, including because of leakingfrom the fluid handling system. A bubble in immersion liquid can lead toimaging errors, for example by interfering with a projection beam duringimaging of the substrate.

It is desirable, for example, to provide a lithographic apparatus inwhich the likelihood of bubble inclusion is at least reduced.

According to an aspect, there is provided a fluid handling structure fora lithographic apparatus, the fluid handling structure having, at aboundary of a space configured to contain immersion fluid to a regionexternal to the fluid handling structure: a meniscus pinning feature toresist passage of immersion fluid in a radially outward direction fromthe space; a plurality of gas supply openings in a linear array at leastpartly surrounding and radially outward of the meniscus pinning feature;and a gas recovery opening radially outward of the plurality of gassupply openings in a linear array.

According to an aspect, there is provided a fluid handling structure fora lithographic apparatus, the fluid handling structure having, at aboundary of a space configured to contain immersion fluid to a regionexternal to the fluid handling structure: a meniscus pinning feature toresist passage of immersion fluid in a radially outward direction fromthe space; an opening of a gas knife at least partly surrounding andradially outward of the meniscus pinning feature; and at least one gasrecovery opening radially outward of the opening of the gas knife, theat least one gas recovery opening comprising a plurality of gas recoveryopenings of a similar or the same size.

According to an aspect, there is provided a fluid handling structure fora lithographic apparatus, the fluid handling structure having, at aboundary of a space configured to contain immersion fluid to a regionexternal to the fluid handling structure: a meniscus pinning feature toresist passage of immersion fluid in a radially outward direction fromthe space; an opening of a gas knife at least partly surrounding andradially outward of the meniscus pinning feature; and at least one gasrecovery opening radially outward of the opening of the gas knife, theat least one gas recovery opening comprising a plurality of gas recoveryopenings in a periodic pattern along a line.

According to an aspect, there is provided a fluid handling structure fora lithographic apparatus, the fluid handling structure having, at aboundary of a space configured to contain immersion fluid to a regionexternal to the fluid handling structure: a meniscus pinning feature toresist passage of immersion fluid in a radially outward direction fromthe space; an opening of a gas knife at least partly surrounding andradially outward of the meniscus pinning feature; and at least one gasrecovery opening radially outward of the opening of the gas knife, theat least one gas recovery opening comprising a plurality of gas recoveryopenings equidistantly spaced apart.

According to an aspect, there is provided a device manufacturing method,comprising: projecting a patterned beam of radiation through animmersion liquid confined to a space between a projection system and asubstrate; providing gas through a plurality of gas supply openings in alinear array to a position adjacent a meniscus of the immersion liquid;and recovering liquid which passes through adjacent gas supply openingsof the plurality of gas supply openings in a linear array through a gasrecovery opening radially outward of the plurality of gas supplyopenings in a linear array.

According to an aspect, there is provided a device manufacturing method,comprising: projecting a patterned beam of radiation through animmersion liquid confined to a space between a projection system and asubstrate; providing gas through an opening of a gas knife to a positionadjacent a meniscus of the immersion liquid; and recovering liquid whichpasses the opening of the gas knife through at least one gas recoveryopening radially outward of the opening of the gas knife, the at leastone gas recovery opening comprising a plurality of gas recovery openingsof a similar or the same size.

According to an aspect, there is provided a device manufacturing method,comprising: projecting a patterned beam of radiation through animmersion liquid confined to a space between a projection system and asubstrate; providing gas through an opening of a gas knife to a positionadjacent a meniscus of the immersion liquid; and recovering liquid whichpasses the opening of the gas knife through at least one gas recoveryopening radially outward of the opening of the gas knife, the at leastone gas recovery opening comprising a plurality of gas recovery openingsin a periodic pattern along a line.

According to an aspect, there is provided a device manufacturing method,comprising: projecting a patterned beam of radiation through animmersion liquid confined to a space between a projection system and asubstrate; providing gas through an opening of a gas knife to a positionadjacent a meniscus of the immersion liquid; and recovering liquid whichpasses the opening of the gas knife through at least one gas recoveryopening radially outward of the opening of the gas knife, the at leastone gas recovery opening comprising a plurality of gas recovery openingsequidistantly spaced apart.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIGS. 2 and 3 depict a liquid supply system for use in a lithographicprojection apparatus;

FIG. 4 depicts a further liquid supply system for use in a lithographicprojection apparatus;

FIG. 5 depicts a further liquid supply system for use in a lithographicprojection apparatus;

FIG. 6 depicts, in cross-section, a further liquid supply system for usein a lithographic projection apparatus;

FIG. 7 depicts, in plan, a liquid supply system for use in alithographic projection apparatus;

FIG. 8 depicts, in plan, a liquid supply system for use in alithographic projection apparatus;

FIG. 9 is a graph of extracted water flow on the y axis versus effectiveflow per surface area on the x axis for four different arrangements ofextraction openings;

FIG. 10 is a graph of radial distance on the x axis vs pressure on the yaxis;

FIG. 11 is a graph of lateral distance on the x axis vs pressure on they axis; and

FIG. 12 depicts, in plan, a liquid supply system for use in alithographic projection apparatus.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus comprises:

-   -   an illumination system (illuminator) IL configured to condition        a radiation beam B (e.g. UV radiation or DUV radiation);    -   a support structure (e.g. a mask table) MT constructed to        support a patterning device (e.g. a mask) MA and connected to a        first positioner PM configured to accurately position the        patterning device MA in accordance with certain parameters;    -   a support table, e.g. a sensor table to support one or more        sensors or a substrate table WT constructed to hold a substrate        (e.g. a resist-coated substrate) W, connected to a second        positioner PW configured to accurately position the surface of        the table, for example of a substrate W, in accordance with        certain parameters; and    -   a projection system (e.g. a refractive projection lens system)        PS configured to project a pattern imparted to the radiation        beam B by patterning device MA onto a target portion C (e.g.        comprising one or more dies) of the substrate W.

The illumination system IL may include various types of opticalcomponents, such as refractive, reflective, magnetic, electromagnetic,electrostatic or other types of optical components, or any combinationthereof, for directing, shaping, or controlling radiation.

The support structure MT holds the patterning device MA. It holds thepatterning device MA in a manner that depends on the orientation of thepatterning device MA, the design of the lithographic apparatus, andother conditions, such as for example whether or not the patterningdevice MA is held in a vacuum environment. The support structure MT canuse mechanical, vacuum, electrostatic or other clamping techniques tohold the patterning device MA. The support structure MT may be a frameor a table, for example, which may be fixed or movable as required. Thesupport structure MT may ensure that the patterning device MA is at adesired position, for example with respect to the projection system PS.Any use of the terms “reticle” or “mask” herein may be consideredsynonymous with the more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device MA may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two or more tables(or stage or support), e.g., two or more substrate tables or acombination of one or more substrate tables and one or more sensor ormeasurement tables. In such “multiple stage” machines the multipletables may be used in parallel, or preparatory steps may be carried outon one or more tables while one or more other tables are being used forexposure. The lithographic apparatus may have two or more patterningdevice tables (or stages or support) which may be used in parallel in asimilar manner to substrate, sensor and measurement tables.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source SO and the lithographic apparatus may beseparate entities, for example when the source SO is an excimer laser.In such cases, the source SO is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source SO may be an integral part of thelithographic apparatus, for example when the source SO is a mercurylamp. The source SO and the illuminator IL, together with the beamdelivery system BD if required, may be referred to as a radiationsystem.

The illuminator IL may comprise an adjuster AD for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator IL can be adjusted. In addition, the illuminator IL maycomprise various other components, such as an integrator IN and acondenser CO. The illuminator IL may be used to condition the radiationbeam, to have a desired uniformity and intensity distribution in itscross-section. Similar to the source SO, the illuminator IL may or maynot be considered to form part of the lithographic apparatus. Forexample, the illuminator IL may be an integral part of the lithographicapparatus or may be a separate entity from the lithographic apparatus.In the latter case, the lithographic apparatus may be configured toallow the illuminator IL to be mounted thereon. Optionally, theilluminator IL is detachable and may be separately provided (forexample, by the lithographic apparatus manufacturer or anothersupplier).

The radiation beam B is incident on the patterning device (e.g., mask)MA, which is held on the support structure (e.g., mask table) MT, and ispatterned by the patterning device MA. Having traversed the patterningdevice MA, the radiation beam B passes through the projection system PS,which focuses the beam onto a target portion C of the substrate W. Withthe aid of the second positioner PW and position sensor IF (e.g. aninterferometric device, linear encoder or capacitive sensor), thesubstrate table WT can be moved accurately, e.g. so as to positiondifferent target portions C in the path of the radiation beam B.Similarly, the first positioner PM and another position sensor (which isnot explicitly depicted in FIG. 1) can be used to accurately positionthe patterning device MA with respect to the path of the radiation beamB, e.g. after mechanical retrieval from a mask library, or during ascan. In general, movement of the support structure MT may be realizedwith the aid of a long-stroke module (coarse positioning) and ashort-stroke module (fine positioning), which form part of the firstpositioner PM. Similarly, movement of the substrate table WT may berealized using a long-stroke module and a short-stroke module, whichform part of the second positioner PW. In the case of a stepper (asopposed to a scanner) the support structure MT may be connected to ashort-stroke actuator only, or may be fixed. Patterning device MA andsubstrate W may be aligned using patterning device alignment marks M1,M2 and substrate alignment marks P1, P2. Although the substratealignment marks as illustrated occupy dedicated target portions, theymay be located in spaces between target portions C (these are known asscribe-lane alignment marks). Similarly, in situations in which morethan one die is provided on the patterning device MA, the patterningdevice alignment marks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

-   -   1. In step mode, the support structure MT and the substrate        table WT are kept essentially stationary, while an entire        pattern imparted to the radiation beam B is projected onto a        target portion C at one time (i.e. a single static exposure).        The substrate table WT is then shifted in the X and/or Y        direction so that a different target portion C can be exposed.        In step mode, the maximum size of the exposure field limits the        size of the target portion C imaged in a single static exposure.    -   2. In scan mode, the support structure MT and the substrate        table WT are scanned synchronously while a pattern imparted to        the radiation beam B is projected onto a target portion C (i.e.        a single dynamic exposure). The velocity and direction of the        substrate table WT relative to the support structure MT may be        determined by the (de-)magnification and image reversal        characteristics of the projection system PS. In scan mode, the        maximum size of the exposure field limits the width (in the        non-scanning direction) of the target portion C in a single        dynamic exposure, whereas the length of the scanning motion        determines the height (in the scanning direction) of the target        portion C.    -   3. In another mode, the support structure MT is kept essentially        stationary holding a programmable patterning device, and the        substrate table WT is moved or scanned while a pattern imparted        to the radiation beam is projected onto a target portion C. In        this mode, generally a pulsed radiation source is employed and        the programmable patterning device is updated as required after        each movement of the substrate table WT or in between successive        radiation pulses during a scan. This mode of operation can be        readily applied to maskless lithography that utilizes        programmable patterning device, such as a programmable mirror        array of a type as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

Arrangements for providing liquid between a final element of theprojection system PS and the substrate can be classed into three generalcategories. These are the bath type arrangement, the so-called localizedimmersion system and the all-wet immersion system. In a bath typearrangement substantially the whole of the substrate W and optionallypart of the substrate table WT is submersed in a bath of liquid.

A localized immersion system uses a liquid supply system in which liquidis only provided to a localized area of the substrate. The space filledby liquid is smaller in plan than the top surface of the substrate andthe area filled with liquid remains substantially stationary relative tothe projection system PS while the substrate W moves underneath thatarea. FIGS. 2-7 show different supply devices which can be used in sucha system. A sealing feature is present to seal liquid to the localizedarea. One way which has been proposed to arrange for this is disclosedin PCT patent application publication no. WO 99/49504.

In an all wet arrangement the liquid is unconfined. The whole topsurface of the substrate and all or part of the substrate table iscovered in immersion liquid. The depth of the liquid covering at leastthe substrate is small. The liquid may be a film, such as a thin film,of liquid on the substrate. Immersion liquid may be supplied to or inthe region of a projection system and a facing surface facing theprojection system (such a facing surface may be the surface of asubstrate and/or a substrate table). Any of the liquid supply devices ofFIGS. 2-5 can also be used in such a system. However, a sealing featureis not present, not activated, not as efficient as normal or otherwiseineffective to seal liquid to only the localized area.

As illustrated in FIGS. 2 and 3, liquid is supplied by at least oneinlet onto the substrate, desirably along the direction of movement ofthe substrate relative to the final element. Liquid is removed by atleast one outlet after having passed under the projection system. As thesubstrate is scanned beneath the element in a −X direction, liquid issupplied at the +X side of the element and taken up at the −X side. FIG.2 shows the arrangement schematically in which liquid is supplied viainlet and is taken up on the other side of the element by outlet whichis connected to a low pressure source. In the illustration of FIG. 2 theliquid is supplied along the direction of movement of the substraterelative to the final element, though this does not need to be the case.Various orientations and numbers of in- and out-lets positioned aroundthe final element are possible; one example is illustrated in FIG. 3 inwhich four sets of an inlet with an outlet on either side are providedin a regular pattern around the final element. Note that the directionof flow of the liquid is shown by arrows in FIGS. 2 and 3.

A further immersion lithography solution with a localized liquid supplysystem is shown in FIG. 4. Liquid is supplied by two groove inlets oneither side of the projection system PS and is removed by a plurality ofdiscrete outlets arranged radially outwardly of the inlets. The inletscan be arranged in a plate with a hole in its centre and through whichthe projection beam is projected. Liquid is supplied by one groove inleton one side of the projection system PS and removed by a plurality ofdiscrete outlets on the other side of the projection system PS, causinga flow of a thin film of liquid between the projection system PS and thesubstrate W. The choice of which combination of inlet and outlets to usecan depend on the direction of movement of the substrate W (the othercombination of inlet and outlets being inactive). Note that thedirection of flow of fluid and of the substrate is shown by arrows inFIG. 4.

Another arrangement which has been proposed is to provide the liquidsupply system with a liquid confinement structure which extends along atleast a part of a boundary of the space between the final element of theprojection system and the substrate table. Such an arrangement isillustrated in FIG. 5.

FIG. 5 schematically depicts a localized liquid supply system or fluidhandling structure 12, which extends along at least a part of a boundaryof the space between the final element of the projection system and thesubstrate table WT or substrate W. (Please note that reference in thefollowing text to surface of the substrate W also refers in addition orin the alternative to a surface of the substrate table, unless expresslystated otherwise.) The fluid handling structure 12 is substantiallystationary relative to the projection system in the XY plane thoughthere may be some relative movement in the Z direction (in the directionof the optical axis). In an embodiment, a seal is formed between thefluid handling structure 12 and the surface of the substrate W and maybe a contactless seal such as a gas seal (such a system with a gas sealis disclosed in European patent application publication no.EP-A-1,420,298) or liquid seal.

The fluid handling structure 12 at least partly contains liquid in thespace 11 between a final element of the projection system PS and thesubstrate W. A contactless seal 16 to the substrate W may be formedaround the image field of the projection system PS so that liquid isconfined within the space between the substrate W surface and the finalelement of the projection system PS. The space 11 is at least partlyformed by the fluid handling structure 12 positioned below andsurrounding the final element of the projection system PS. Liquid isbrought into the space below the projection system PS and within thefluid handling structure 12 by liquid inlet 13. The liquid may beremoved by liquid outlet 13. The fluid handling structure 12 may extenda little above the final element of the projection system. The liquidlevel rises above the final element so that a buffer of liquid isprovided. In an embodiment, the fluid handling structure 12 has an innerperiphery that at the upper end closely conforms to the shape of theprojection system or the final element thereof and may, e.g., be round.At the bottom, the inner periphery closely conforms to the shape of theimage field, e.g., rectangular, though this need not be the case.

The liquid may be contained in the space 11 by a gas seal 16 which,during use, is formed between the bottom of the fluid handling structure12 and the surface of the substrate W. The gas seal is formed by gas.The gas in the gas seal is provided under pressure via inlet 15 to thegap between the fluid handling structure 12 and substrate W. The gas isextracted via outlet 14. The overpressure on the gas inlet 15, vacuumlevel on the outlet 14 and geometry of the gap are arranged so thatthere is a high-velocity gas flow 16 inwardly that confines the liquid.The force of the gas on the liquid between the fluid handling structure12 and the substrate W contains the liquid in a space 11. Theinlets/outlets may be annular grooves which surround the space 11. Theannular grooves may be continuous or discontinuous. The flow of gas 16is effective to contain the liquid in the space 11. Such a system isdisclosed in U.S. patent application publication No. US 2004-0207824,which is hereby incorporated by reference in its entirety. In anembodiment, the fluid handling structure 12 does not have a gas seal.

FIG. 6 illustrates a fluid handling structure 12 which is part of aliquid supply system. The fluid handling structure 12 extends around theperiphery (e.g. circumference) of the final element of the projectionsystem PS.

A plurality of openings 20 in the surface which in part defines thespace 11 provide the liquid to the space 11. The liquid passes throughopenings 29, 20 in side walls 28, 22 respectively through respectivechambers 24, 26 prior to entering the space 11.

A seal is provided between the bottom of the fluid handling structure 12and a facing surface, e.g. the substrate W, or a substrate table WT, orboth. In FIG. 6 a seal device is configured to provide a contactlessseal and is made up of several components. Radially outwardly from theoptical axis of the projection system PS, there is provided a (optional)flow control plate 51 which extends into the space 11. The control plate51 may have an opening 55 to permit flow liquid therethrough; theopening 55 may be beneficial if the control plate 51 is displaced in theZ direction (e.g., parallel to the optical axis of the projection systemPS). Radially outwardly of the flow control plate 51 on the bottomsurface of the fluid handling structure 12 facing (e.g., opposite) thefacing surface, e.g., the substrate W, may be an opening 180. Theopening 180 can provide liquid in a direction towards the facingsurface. During imaging this may be useful in preventing bubbleformation in the immersion liquid by filling a gap between the substrateW and substrate table WT with liquid.

Radially outwardly of the opening 180 may be an extractor assembly 70 toextract liquid from between the fluid handling structure 12 and thefacing surface. The extractor assembly 70 may operate as a single phaseor as a dual phase extractor. The extractor assembly 70 acts as ameniscus pinning feature. The meniscus pinning feature may define, inuse, a meniscus between the fluid handling structure and facing surface.The meniscus may be the outer extent, or boundary, at least under thefluid handing structure, of the liquid confined by the fluid handlingstructure.

Radially outwardly of the extractor assembly may be a gas knife 90. Anarrangement of the extractor assembly and gas knife is disclosed indetail in United States patent application publication no. US2006/0158627 incorporated herein in its entirety by reference.

The extractor assembly 70 as a single phase extractor may comprise aliquid removal device, extractor or inlet such as the one disclosed inU.S. patent application publication No. US 2006-0038968, incorporatedherein in its entirety by reference. In an embodiment, the liquidremoval device 70 comprises an inlet which is covered in a porousmaterial 111 which is used to separate liquid from gas to enablesingle-liquid phase liquid extraction. An under pressure in chamber 121is chosen is such that the meniscuses formed in the holes of the porousmaterial 111 substantially prevent ambient gas from being drawn into thechamber 121 of the liquid removal device 70. However, when the surfaceof the porous material 111 comes into contact with liquid there is nomeniscus to restrict flow and the liquid can flow freely into thechamber 121 of the liquid removal device 70.

The porous material 111 has a large number of small holes each with adimension, e.g. a width, such as a diameter, in the range of 5 to 50micrometers. The porous material 111 may be maintained at a height inthe range of 50 to 300 micrometers above a surface, such as a facingsurface, from which liquid is to be removed, e.g. the surface of asubstrate W. In an embodiment, porous material 111 is at least slightlyliquidphilic, i.e. having a dynamic contact angle of less than or equalto 90°, desirably less than or equal to 85° or desirably less than orequal to 80°, to the immersion liquid, e.g. water.

In an embodiment, the liquid supply system has an arrangement to dealwith variations in the level of the liquid. This is so that liquid whichbuilds up between the projection system PS and the liquid confinementstructure 12 (forming, e.g., a meniscus 400) can be dealt with and doesnot escape. One way of dealing with this liquid is to provide alyophobic (e.g., hydrophobic) coating. The coating may form a bandaround the top of the fluid handling structure 12 surrounding theopening and/or around the last optical element of the projection systemPS. The coating may be radially outward of the optical axis of theprojection system PS. The lyophobic (e.g., hydrophobic) coating helpskeep the immersion liquid in the space 11. An additional or alternativeway of dealing with this liquid is to provide an outlet 201 to removeliquid reaching a certain point (e.g., height) relative to the liquidconfinement structure 12 and/or projection system PS.

Another localized area arrangement is a fluid handling structure whichmakes use of a gas drag principle. The so-called gas drag principle hasbeen described, for example, in U.S. patent application publication Nos.US 2008-0212046, US 2009-0279060 and US 2009-0279062. In that system theextraction holes are arranged in a shape which may desirably have acorner. The corner may be aligned with a preferred direction ofmovement, such as the stepping or the scanning direction. This reducesthe force on the meniscus between two openings in the surface of thefluid handing structure for a given speed in the preferred directioncompared to if the two outlets were aligned perpendicular to thepreferred direction. However, an embodiment of the invention may beapplied to a fluid handling system which in plan has any shape, or has acomponent such as the extraction openings arranged in any shape. Such ashape in a non-limiting list may include an ellipse such as a circle, arectilinear shape such as a rectangle, e.g. a square, or a parallelogramsuch as a rhombus or a cornered shape with more than four corners suchas a four or more pointed star.

In a variation of the system of US 2008/0212046 A1, to which anembodiment of the present invention may relate, the geometry of thecornered shape in which the openings are arranged allows sharp corners(between about 60° and 90°, desirably between 75° and 90° and mostdesirably between 75° and 85°) to be present for the corners alignedboth in the scan and in the stepping directions. This allows increasedspeed in the direction of each aligned corner. This is because thecreation of liquid droplets due to an unstable meniscus, for example inexceeding a critical speed, in the scanning direction is reduced. Wherecorners are aligned with both the scanning and stepping directions,increased speed may be achieved in those directions. Desirably the speedof movement in the scanning and stepping directions may be substantiallyequal.

FIG. 7 illustrates schematically and in plan meniscus pinning featuresof a fluid handling system or of a fluid handling structure 12 having anextractor embodying the gas drag principle and to which an embodiment ofthe present invention may relate. The features of a meniscus pinningdevice are illustrated which may, for example, replace the meniscuspinning arrangement 14, 15, 16 of FIG. 5 or at least the extractorassembly 70 shown in FIG. 6. The meniscus pinning device of FIG. 7 is aform of extractor. The meniscus pinning device comprises a plurality ofdiscrete openings 50. Each opening 50 is illustrated as being circular,though this is not necessarily the case. Indeed one or more of theopenings 50 may be one or more selected from: circular, elliptical,rectilinear (e.g. square, or rectangular), triangular, etc. and one ormore openings may be elongate. Each opening has, in plan, a lengthdimension (i.e. in the direction from one opening to the adjacentopening) of greater than or equal to 0.2 mm, greater than or equal to0.5 mm, or greater than or equal to 1 mm. In an embodiment, the lengthdimension is selected from the range of 0.1 mm to 10 mm or selected fromthe range of 0.25 mm to 2 mm. In an embodiment, the width of eachopening is selected from the range of 0.1 mm to 2 mm. In an embodimentthe width of each opening is selected from the range of 0.2 mm to 1 mm.In an embodiment the length dimension is selected from the range of 0.2mm to 0.5 mm or selected from the range of 0.2 mm to 0.3 mm. Inletopenings like those of FIG. 6 (labeled 180) may be provided radiallyinwardly of the openings 50.

Each of the openings 50 of the meniscus pinning device of FIG. 7 may beconnected to a separate under pressure source. Alternatively oradditionally, each or a plurality of the openings 50 may be connected toa common chamber or manifold (which may be annular) which is itself heldat an under pressure. In this way a uniform under pressure at each or aplurality of the openings 50 may be achieved. The openings 50 can beconnected to a vacuum source and/or the atmosphere surrounding the fluidhandling system (or confinement structure) may be increased in pressureto generate the desired pressure difference.

In the embodiment of FIG. 7 the openings are fluid extraction openings.Each opening is an inlet for the passage of gas, liquid or a two phasefluid of gas and liquid, into the fluid handling system. Each inlet maybe considered to be an outlet from the space 11.

The openings 50 are formed in a surface of a fluid handling structure12. The surface faces the substrate W and/or substrate table WT, in use.In an embodiment the openings are in a flat surface of the fluidhandling structure 12. In an embodiment, a ridge may be present on thebottom surface of the substrate member. At least one of the openings maybe in the ridge. The openings 50 may be defined by needles or tubes. Thebodies of some of the needles, e.g., adjacent needles, may be joinedtogether. The needles may be joined together to form a single body. Thesingle body may form the cornered shape.

The openings 50 are the end of a tube or elongate passageway, forexample. Desirably the openings are positioned such that in use they aredirected, desirably face, to the facing surface, e.g. the substrate W.The rims (i.e. outlets out of a surface) of the openings 50 may besubstantially parallel to a top surface of a part of the facing surface.An elongate axis of the passageway to which the opening 50 is connectedmay be substantially perpendicular (within +/−45°, desirably within 35°,25° or even 15° from perpendicular) to the top of the facing surface,e.g., the top surface of the substrate W.

Each opening 50 is designed to extract a mixture of liquid and gas. Theliquid is extracted from the space 11 whereas the gas is extracted fromthe atmosphere on the other side of the openings 50 to the liquid. Thiscreates a gas flow as illustrated by arrows 100 and this gas flow iseffective to pin the meniscus 320 between the openings 50 substantiallyin place as illustrated in FIG. 7. The gas flow helps maintain theliquid confined by momentum blocking, by a gas flow induced pressuregradient and/or by drag (shear) of the gas (e.g., air) flow on theliquid.

The openings 50 surround the space to which the fluid handling structuresupplies liquid. The openings 50 may be distributed in an undersurfaceof the fluid handling structure. The openings 50 may be substantiallycontinuously spaced around the space (although the spacing betweenadjacent openings 50 may vary). In an embodiment, liquid is extractedall the way around the cornered shape and is extracted substantially atthe point at which it impinges on the cornered shape. This is achievedbecause the openings 50 are formed all the way around the space (in thecornered shape). In this way the liquid may be confined to the space 11.The meniscus may be pinned by the openings 50, during operation.

As can be seen from FIG. 7, the openings 50 are positioned so as toform, in plan, a cornered shape (i.e. a shape with corners 52). In thecase of FIG. 7 this is in the shape of a rhombus, desirably a square,with curved edges or sides 54. The edges 54, if curved, have a negativeradius. The edges 54 may curve towards the center of the cornered shapein areas away from the corners 52. An embodiment of the invention may beapplied to any shape, in plan, including, but not limited to the shapeillustrated, for example, a rectilinear shape, e.g. a rhombus, a squareor rectangle, or a circular shape, a triangular shape, a star shape, anelliptical shape, etc.

The cornered shape has principal axes 110, 120 aligned with the majordirections of travel of the substrate W under the projection system PS.This helps ensure that, below a critical scan speed, the maximum scanspeed is faster than if the openings 50 were arranged in a circularshape. This is because the force on the meniscus between two openings 50is reduced with a factor cos θ. Here θ is the angle of the lineconnecting the two openings 50 relative to the direction in which thesubstrate W is moving.

The use of a square cornered shape allows movement in the step andscanning directions to be at an equal maximum speed. This may beachieved by having each of the corners 52 of the shape aligned with thescanning and stepping directions 110, 120. If movement in one of thedirections, for example the scan direction is preferred to be fasterthan movement in the step direction then a rhombus shape could be used.In such an arrangement the primary axis of the rhombus may be alignedwith the scan direction. For a rhombic shape, although each of thecorners may be acute, the angle between two adjacent sides of therhombus, for example in the stepping direction, may be obtuse, i.e. morethan 90° (for example selected from the range of about 90° to 120°, inan embodiment selected from the range of about 90° to 105°, in anembodiment selected from the range of about 85° to 105°).

Throughput can be optimized by making the primary axis of the shape ofthe openings 50 aligned with the major direction of travel of thesubstrate (usually the scan direction) and to have a second axis alignedwith the other major direction of travel of the substrate (usually thestep direction). It will be appreciated that any arrangement in which θis different to 90° will give an advantage in at least one direction ofmovement. Thus, exact alignment of the principal axes with the majordirections of travel is not vital.

An advantage of providing the edges with a negative radius is that thecorners may be made sharper. An angle selected from the range of 75 to85° or even lower may be achievable for both the corners 52 aligned withthe scan direction and the corners 52 aligned with the step direction.If it were not for this feature then in order for the corners 52 alignedin both directions to have the same angle, those corners would have tohave 90°. If less than 90° were desired it would be necessary to selectone direction to have corners with less than 90° with the result thatthe other corner would have an angle of greater than 90°.

There may be no meniscus pinning feature radially inwardly of theopenings 50. The meniscus is pinned between the openings 50 with dragforces induced by gas flow into the openings 50. A gas drag velocity ofgreater than or equal to about 15 m/s, desirably about 20 m/s should besufficient. The amount of evaporation of liquid from the substrate maybe reduced thereby reducing both splashing of liquid as well as thermalexpansion/contraction effects.

In an embodiment, at least thirty-six (36) discrete openings 50 eachwith a diameter of 1 mm and separated by 3.9 mm may be effective to pina meniscus. In an embodiment, one hundred and twelve (112) openings 50are present. The openings 50 may be square, with a length of a side of0.5 mm, 0.3 mm, 0.25 mm, 0.2 mm, 0.15 mm, 0.1 mm or 0.05 mm. The totalgas flow in such a system may be of the order of 100 l/min. In anembodiment the total gas flow is selected from the range of 50 l/min to130 l/min, in an embodiment, 70 l/min to 130 l/min.

Other geometries of the bottom of the fluid handling structure 12 arepossible. For example, any of the structures disclosed in U.S. patentapplication publication no. US 2004-0207824 or U.S. patent applicationpublication no. US 2010-0313974 could be used in an embodiment of thepresent invention.

Localized area fluid handling structures 12 such as those describedabove, with reference to FIGS. 2-7, may suffer from bubble inclusioninto the space 11. As can be seen, a meniscus 320 extends between thefluid handling structure 12 and the surface under the fluid handlingstructure 12. This meniscus 320 illustrated in FIGS. 5 and 6 defines theedge of the space 11. When the meniscus 320 and a droplet collide on thesurface, for example a droplet of liquid which has escaped the space 11,a bubble of gas may be included into the space 11. Inclusion of a bubbleinto the space 11 is detrimental because a bubble of gas can lead to animaging error. A droplet is usually left behind on the surface in one ofat least three circumstances: (a) when the liquid handling device islocated over the edge of a substrate W when there is relative movementbetween the fluid handling structure 12 and the substrate W; (b) whenthe fluid handling structure 12 is located over a step change in heightof the facing surface facing the liquid confinement structure when thereis relative movement between the fluid handling structure 12 and thefacing surface; and/or (c) due to too high relative speed between thefluid handling structure 12 and the facing surface, for example when themeniscus becomes unstable, e.g. by exceeding the critical scan speed ofthe facing surface. One or more further features radially outward of themeniscus pinning feature, such as a gas knife, can be used to catch anyescaped liquid.

In a fluid handling structure 12 such as that described in US2010/0313974, a gas knife in the form of a slit opening (e.g. acontinuous linear opening) is provided around the openings 50. A gasknife in the form of a slit opening may also be provided around theextractor 70 of the FIG. 6 embodiment. A gas knife in the form of a slitopening might typically have a width of 50 μm. However, such an openingcan be difficult to manufacture and this can lead to variations in thepressure particularly radially inwardly of the gas knife, around theperiphery (e.g., circumference) of the meniscus pinning feature.Additionally, a gas knife in the form of a slit may be particularlysensitive to the presence of contamination. This again leads toinstability in under pressure around the periphery of the meniscuspinning feature. An embodiment of the present invention addresses one ormore of these (and additionally or alternatively other) problems.

In an embodiment shown in FIGS. 6 and 7, a plurality of gas supplyopenings 61 (i.e. discrete apertures) are provided in a linear array.Relative to the space, the gas supply openings 61 are provided radiallyoutward of the meniscus pinning feature (the extractor 70 and openings50, respectively). The linear array made by the gas supply openings 61may be substantially parallel to the lines joining the openings 50. Inuse, the gas supply openings 61 are connected to an over pressure andform a gas knife (supplying a gas, e.g. air) surrounding the meniscuspinning device. The plurality of gas supply openings 61 in a lineararray (e.g. a one or two dimensional linear array) at least partlysurround the meniscus pinning feature.

One example of a linear array is a line. One example of a linear arraycomprises two or more rows of openings. The openings may be periodicallyarranged along the linear array. For example the openings along the rowsmay be staggered. In one or more of the rows of openings, each of theopenings may be aligned in a line. The openings in two of the rows maybe staggered with respect to each other (i.e. two lines of holes).

In an embodiment the plurality of gas supply openings 61 are of asimilar, e.g. the same, size. In an embodiment, the gas supply openings61 are all within a percentage, e.g. 5%, of a pre-determined size. In anembodiment the plurality of gas supply openings 61 are arranged in aperiodic pattern along a line i.e. a repeating series of holes withdifferent gaps between each of the holes in the series, for example twoholes spaced closely apart followed by a gap and then two holes spacedclosely apart followed by a gap, etc. In an embodiment the plurality ofgas supply openings 61 are equidistantly spaced apart. In an embodimenta line along which adjacent openings are arranged is straight. In anembodiment the plurality of gas supply openings 61 are arranged toensure a substantially uniform flow of gas out of the gas supplyopenings 61 per unit length.

In an embodiment, the gas supply openings 61 function to reduce thethickness of a liquid film left on a facing surface, such as thesubstrate W or substrate table WT, in passage under the fluid handlingstructure 12, for example a droplet moving relatively towards meniscus320 from radially outward of the linear array, or a droplet relativelymoving from the meniscus 320 radially outwardly. With the substantiallysame flow rate through the plurality of gas supply openings 61 (forexample with a diameter of 90 μm and 200 μm pitch) a higher averagepressure peak under the openings may be achieved than for a slit gasknife with a slit width of, for example, 50 μm, using the same flowrate. The discrete gas supply openings 61 therefore may cause a thinnerliquid film to be left on the facing surface after passage of the liquidfilm under the fluid handling structure 12. The higher average pressurepeak may result in improved efficiency in stopping droplets movingrelative to the meniscus 320. The higher average pressure peak mayresult in even better performance when the gap between the edge of asubstrate W and the substrate table WT is crossed. When using a slit gasknife, the pressure peak under the slit may collapse because the gasflow out of the slit can be sucked away through the openings 50. Thepressure peak of the plurality of gas supply openings 61 may be lesslikely to be sucked away through openings 50. This may result in betterperformance as the pressure peak is more stable (see FIG. 10, describedlater).

The gas supply openings 61 may help to ensure that the liquid film doesnot break into droplets but rather the liquid is driven towards theopenings 50 and extracted. In an embodiment the gas supply openings 61operate to prevent the formation of a film. The linear array in whichthe gas supply openings 61 are arranged generally follows the line ofthe meniscus pinning feature (e.g. openings 50). Thus the distancebetween adjacent meniscus pinning features (e.g. openings 50) and thegas supply openings 61 is within 0.5 mm to 4.0 mm, desirably 2 mm to 3mm. The distance between the gas supply openings 61 and openings 50 canbe small while still reducing the risk of bubbles derived from dropletcollision with the meniscus 320, compared to a slit gas knife.

In an embodiment the linear array in which the gas supply openings 61are arranged is substantially parallel to the line of the meniscuspinning feature (e.g. openings 50). In an embodiment a substantiallyconstant separation between adjacent ones of the meniscus pinningfeature (e.g. openings 50) and the gas supply openings 61 is maintained.

In an embodiment the plurality of gas supply openings 61 in a lineararray acts as a gas knife.

A slit may be formed in an immersion fluid handling structure 12, whichmight be made of stainless steel, by bolting together blocks of metalwith a suitable distance between the blocks to form the slit. However,it may be difficult to achieve the desired and/or a constant slit width.By contrast, the discrete gas supply outlets 61 may be formed byablation, for example, using a laser to burn material away. This mayresult in greater uniformity of opening cross-section, dimension andlocation. It may be possible to drill the openings (which are desirablyround, in cross section, because this is easiest to manufacture) with anaccuracy of 5%. By contrast, a slit of 50 μm may have a tolerance of+/−10 μm which is about +/−20%.

A plurality of discrete gas supply openings 61 in a linear array may notbe as sensitive to contamination or variation in size as a slit gasknife because the opening is larger (e.g. 100 μm) compared to a slitwidth (of say 50 μm).

A gas knife should have one or more sharp edges to help ensure good gasknife functionality. The edge may be damaged by contact with an object(for example with the substrate, which may happen during zeroing of theworking distance (the distance between the fluid handling structure 12and the facing surface)).

As a result of potential better manufacturability and lesssusceptibility to contamination and damage, the use of discrete gassupply openings 61 instead of a slit gas knife may result in betteruniformity of pressure on the meniscus 320. In practice, an increase ingas flow through the discrete openings 61 compared to that which can beprovided using a slit opening may be achieved (even though theoreticallya slit might be expected to perform better). At a corner of the shape ofa gas knife feature (e.g. arrangement of discrete openings or a slit),in plan, a problem can arise with a slit gas knife which may not occurwith the use of discrete gas supply openings 61.

Using discrete openings, the flow rate out of the discrete gas supplyopenings 61 may be increased by a factor of up to 1.5 compared to theflow out of openings 50 without disturbing the meniscus 320. At such aflow rate an equivalent slit gas knife (i.e. one with the same open areaper unit length) would result in an unstable meniscus 320, particularlywhen crossing the edge of the substrate or a step change in height onthe substrate table WT. However, at such flow settings, for anequivalent discrete gas knife arrangement, the meniscus has greaterstability.

In order for the discrete gas supply openings 61 to exhibit gas knifelike functionality, an open area of less than or equal to 6.0×10⁻⁵ m²per meter length is desirable. This equates to the same open area perunit length as a gas knife with a slit width of 60 μm. In an embodimentthe open area per meter length is less than or equal to 5.0×10⁻⁵ m²,less than or equal to 4.0×10⁻⁵ m² or less than or equal to 3.5×10⁻⁵ m².The lower the open area ratio, the higher the maximum achievablepressure under each opening and the more like a raking action may beachieved. However, if the open area becomes too small the gas knifefunctionality is lost because of the impossibility of reducing the pitchbetween adjacent gas supply openings to less than or equal to 180 μm. Inan embodiment the open area per meter length is greater than or equal to1.0×10⁻⁵ m², greater than or equal to 2.0×10⁻⁵ m², or greater than orequal to 2.5×10⁻⁵ m². Larger open areas are desirable as this allowslarger gas flows and therefore higher achievable pressure.

In an embodiment the gas supply openings 61 are circular (round) incross-section. In an embodiment the diameter or maximum dimension in thecase of a non-circular opening 61 is less than or equal to 125 μm,desirably less than or equal to 115 μm. This equates to an area peropening of at most (calculated for the case of a square opening)1.6×10⁻⁸ m², desirably at most 1.3×10⁻⁸ m². In an embodiment, themaximum hole diameter is 200 μm.

Theoretical calculations indicate that the hole diameter of the gassupply openings 61 should be at least ½ the working distance which isthe distance between the bottom surface of the fluid handling structure12 and the facing surface (e.g. substrate W). A typical distance betweenthe under surface of the fluid handling structure 12 and the facingsurface (working distance or fly height) is 150 μm, indicating a minimumhole diameter of 75 μm in an embodiment. If this requirement is met, thecore of the gas jet exiting the gas supply opening 61, which is notdisturbed by the stagnant environment which the jet penetrates, reachesthe facing surface and so a large pressure gradient is generated.

In an embodiment the discrete gas supply openings 61 have a diameter orminimum dimension in the case of a non round opening 61 of greater thanor equal to 80 μm, more desirably greater than or equal to 90 μm. Across-sectional area of greater than or equal to 5.0×10⁻⁹ m² per meterlength or greater than or equal to 6.4×10⁻⁹ m² per meter length istherefore desirable. This range of hole sizes makes a balance betweenthe ability to manufacture (at the lower size range), and the maximumallowable pitch between adjacent gas supply openings 61 (at the uppersize range). That is, the maximum allowable pitch is related to thepitch which can lead to the minimum pressure being above a predefinedminimum (e.g. 50 mbar) between adjacent openings 61. Additionally, iftoo little material is left between adjacent openings, this can resultin weakness and potential breakage and this leads to a maximum holediameter.

In an embodiment, the pitch between adjacent gas supply openings 61 isgreater than or equal to 180 μm, desirably greater than or equal to 200μm. Conversely, the pitch should be less than or equal to 400 μm,desirably less than or equal to 200 μm, and more desirably less than orequal to 280 μm. These ranges strike a balance between strength andjoining together of gas streams from adjacent openings and therebyprovide a large minimum pressure between openings (of at least 30 mbar,desirably at least 50 mbar).

In an embodiment, in order for the minimum desired pressure betweenadjacent holes of the plurality of gas supply openings 61 in a line tobe achieved, the length of material between adjacent holes should be amaximum of half the distance between the bottom surface of the fluidhandling structure 12 and the facing surface. This gives a minimumlength of material of 75 μm. In an embodiment, the pitch is chosen suchthat gas jets out of each discrete gas supply opening 61 overlap with anadjacent discrete gas supply opening. The gas jet tends to spread outwith a one over four shape. Therefore in an embodiment, for the jets tooverlap the gas supply openings 61 should be less than or equal to 2times ¼ of the working distance apart or ½ the working distance apart orless.

In an embodiment, material present between adjacent openings 61 shouldbe at least 80 μm long, or at least 90 μm long to provide sufficientstrength.

More than or equal to 200 μm of material between adjacent openings 61may be unnecessary and may lead to separation of gas jets and thereby apressure of less than or equal to 30 mbar between openings. In anembodiment at most a distance of 150 μm between adjacent gas supplyopenings 61 may be provided.

In an embodiment, the gas supply openings 61 have a diameter of 125 μmand a pitch of 300 μm which results in an open area of 5.8×10⁻⁵ m² permeter. If the pitch is reduced to 180 μm, the open area rises to9.8×10⁻⁵, but in some circumstances that may be too much and only leavesa length of 55 μm of material between openings 61. In an embodiment theopening 61 diameter is 80 μm, this leads to an open area of 2.79×10⁻⁵ m²per meter with a pitch of 180 μm which is close to equivalent to a slitwidth of 30 μm.

The possible improvement in manufacturability and stability of themeniscus relative to a slit gas knife is beyond the expectation of theinventors and may provide one or more other unexpected benefits asdescribed herein. Holes of larger dimensions, e.g. 100 μm diameter and apitch of 200 μm, for example, can be made with greater consistency andaccuracy than a slit of smaller dimension, say 50 μm. The resulting gasflow may therefore be more predictable and more effective. In addition,because the maximum dimension of an opening of a discrete gas supplyopening 61 (e.g. diameter) is larger than the maximum dimension of aslit gas knife (e.g. slit width), a gas knife comprising a plurality ofdiscrete gas supply openings 61 may be more robust over a larger rangeof working distances and less sensitive to contamination.

In an embodiment a large pressure gradient exists in a direction goingbetween adjacent gas supply openings 61 and this may result in dropletsmoving to the point of lowest pressure between openings 61. Heredroplets can conglomerate. Some droplets may pass at the point of lowestpressure between gas supply openings 61. Therefore, as illustrated incross section in FIG. 6 and in plan in FIG. 8, in an embodiment at leastone extraction opening 210 is provided radially outwardly of theplurality of discrete gas supply openings 61 in a linear array.

In an embodiment the at least one extraction opening 210 may be aplurality of extraction openings 210. In an embodiment at least oneextraction opening 210 is a slit opening (i.e. continuous). Thisembodiment is advantageous in that a droplet, irrespective of where itpasses the plurality of gas supply openings 61, is collected. In anembodiment each space between adjacent gas supply openings 61 has acorresponding extraction opening 210. In an embodiment the extractionopenings 210 are a plurality of gas extraction openings in a lineararray (e.g. a line).

In an embodiment where the at least one extraction opening 210 is aplurality of extraction openings 210, the gas knife may be in the formof a slit or continuous opening. That is, the plurality of gas supplyopenings 61 described in FIG. 8 actually comprise a slit (i.e.continuous) opening.

An advantage of using a plurality of discrete extraction openings 210,irrespective of whether the gas knife is in the form of a slit orplurality of gas supply openings 61, is reduction in flow in order toremove liquid which passes the gas knife. Calculations based onassumptions about the physical quantity of liquid needed to be extractedout of the extraction openings and empirical relationships betweenunderpressure and flow dependent upon opening size and geometry can bemade. Such calculations show that a flow rate of between 10 and 20 l/minshould be provided for a set of discrete extraction openings with adiameter of 80 μm, a pitch of 250 μm and a peripheral length of between200 and 350 mm. In contrast, if the extraction opening 210 is in theform of a slit of 100 μm width, a flow rate of a factor of five timeshigher can be calculated as being required. Experiments show a similarimprovement in flow. FIG. 9 illustrates for four different types ofextraction openings 210 results of extracted water flow on the y axis(in mL per minute) versus effective gas flow per surface area (in nanoliters per minute per mm²). Results for extraction openings 210 with ahole diameter of 100 μm and a pitch of 200 μm are shown as diamonds, theresults for a slit opening with an opening width of 50 μm are shown astriangles, the results for a slit opening with an opening width of 100μm are shown as circles and the results for a slit opening with anopening width of 150 μm are shown as squares. All experiments werecarried out with a working distance between the undersurface of thefluid handling structure and the facing surface of 150 μm. In theexperiment a water droplet was moved under the extraction openings 210and the extracted water flow V and effective flow per surface area Qe/Awas noted. These results show that for a given extracted water flow(i.e. for a given amount of liquid which needs to be extracted by theextraction openings 210) the effective gas flow per surface area of thediscrete extraction openings is a factor of 4 times more efficient thanfor a slit opening with a width of 100 or 150 μm. The effective gas flowper surface area of the discrete extraction openings of the discreteextraction openings is a factor of 2 times more efficient than for aslit opening with a width of 50 μm.

In order to balance the gas flows between the openings 50, the gassupply openings 61 and extraction openings 210, a certain flow rate intothe extraction openings 210 should be provided. The experimental resultsin FIG. 9 show that for a given flow rate into the extraction openings210, the use of discrete extraction openings 210 results in a higherflow rate into the extraction openings 210 which results in moreefficient extraction of liquid. Further advantages are that lower forcesare applied between the fluid handling structure and the facing surface(because of the smaller total area of the openings) and/or that less gasflow can be used. Additionally, discrete openings have less influence onthe pressure peak (see FIG. 10 and related description below) of the gassupply openings 61 than a slit.

An advantage of having a lower extraction flow rate is that the fluidhandling structure is less sensitive to imbalances in flow between theopenings 50, gas supply opening 61 and extraction openings 210.Robustness in terms of sensitivity to the presence of contamination maybe improved. Additionally manufacturability may be improved as it isless time consuming and technically easier to make holes compared to aslit, as described elsewhere. Furthermore, the system may result infewer droplets between the gas supply opening(s) 61 and the outerextraction openings 210. In the case of a plurality of gas supplyopenings 61, droplets of liquid can be steered towards a discreteextraction opening 210 which corresponds in position to the gap betweenthe gas supply openings 61, as described elsewhere. Further, because alower gas flow rate into extraction openings 210 is possible, a lowerstatic force may be applied between the fluid handling structure 12 andthe facing surface (e.g. substrate) which is advantageous in terms ofcontrol of position of the substrate.

A droplet which passes the linear array of gas supply openings 61 willpass at a position of lowest pressure. As a result, the droplet willpass substantially equidistant between adjacent openings 61. Therefore,by positioning of the extraction opening 210 substantially equidistantbetween adjacent openings 61 as described above (i.e. at a positionwhich bisects the space between adjacent openings 61), a droplet whichpasses the linear array of gas supply openings 61 is likely to passunder an extraction opening 210 corresponding to the space through whichthe droplet has moved. As a result, the droplet is likely to beextracted by the extraction opening 210. An extraction takes place ifthe droplet touches the extraction opening 210 and so the effect of thetangential pressure gradient which results in conglomeration of dropletsis advantageous as this leads to larger droplets which are more likelyto touch the extraction openings 210.

The extraction openings 210 may have the same characteristics and/ordimensions as the gas supply openings 61 described above. The at leastone extraction opening 210 may be discontinuous, continuous, a twodimensional linear array (e.g. two substantially parallel lines ofopenings), etc.

In an embodiment, the distance between the at least one extractionopening 210 and the plurality of gas supply openings 61 is at least 0.2mm and at most 1.0 mm. This relatively short distance is advantageousbecause droplets are more likely to be captured. If the distance is tooshort, this can led to interference between the gas flows out of the gassupply openings 61 and into the extraction openings 210 which isundesirable.

The under pressure generated radially inwardly of the plurality ofdiscrete gas supply openings 61 and radially outwardly of the openings50 may be lower and more constant, radially and tangentially, than theunder pressure generated by a gas knife in the form of a slit. FIG. 10illustrates this phenomenon. FIG. 10 (and FIG. 11) is applicable both tothe embodiment without at least one extraction opening 210 (asillustrated in FIG. 7) as well as to the embodiment with at least oneextraction opening 210 (as illustrated in FIG. 8). FIGS. 10 and 11 weredetermined using an embodiment according to FIG. 8.

FIG. 10 plots radial distance on the x axis, with negative numbers beingradially inward of the gas supply openings 61 or gas knife, versusrelative pressure at substrate level on the y axis. An example gas knifewith a slit of 50 μm is shown as dotted lines and shows a maximum underpressure of the order of −50 mbar which decreases towards −10 mbar asthe openings 50 are approached. In contrast, for an example plurality ofdiscrete gas supply openings 61 with a opening diameter of 100 μm and apitch of 200 μm, the minimum pressure is −10 mbar. This is advantageousbecause it may result in a decrease in the attractive force between thefluid handling structure 12 and the facing surface. Additionally, it mayresult in fewer and smaller droplets being present between the openings50 and the discrete gas supply openings 61. That may result in the riskof gas bubbles in the immersion liquid in the space 11 being reduced.Additionally, with the discrete openings 61, the pressure radiallyinward may be relatively constant along the majority of the lengthbetween the opening 50 and the gas supply openings 61. This isadvantageous because the large pressure gradient generated using a slitgas knife may result in turbulent flow and this may be avoided using thediscrete openings 61.

The experiments of FIG. 10 were carried out with a distance between theunder surface of the fluid handling system 12 and the facing surface(e.g. substrate) being 150 μm, with a flow rate out of the openings 50of 30 l/min, a flow rate through the gas knife or gas supply openings 61of 45 l/min and a flow rate from extraction openings of 30 l/min.

FIG. 11 shows the relative change in pressure along the length of thelinear array of the plurality of discrete gas supply openings 61. Thesame operating conditions as described above with relation to FIG. 10are present. As can be seen, a maximum pressure is achieved under eachgas supply opening 61 with a minimum pressure reached between adjacentopenings 61. As can be seen, there is a drop in pressure betweenadjacent gas supply openings 61. Advantageously the drop in pressure isless than a drop to zero so that a force will be felt by a droplet atthat location. This is advantageous because there is then a resistanceto the passing of a droplet all around the meniscus pinning feature(because a positive pressure exists under the gas supply openings 61 allthe way around the linear array of gas supply openings 61).

The pressure profile such as in FIG. 11 is advantageous over that of aslit gas knife in that the pressure profile has a series of peaks andtroughs sufficient to aggregate small droplets of harmless size. Thismeans that pressure radially outward of the meniscus 320 can fluctuateas gas can more easily pass the pressure profile. As a result themeniscus 320 may be stabilized which may mean less liquid loss from themeniscus 320. Additionally, when the gap between the edge of thesubstrate W and the substrate table WT passes under the plurality ofdiscrete openings 61, immersion liquid in that gap may be less likely tobe forced out and so the risk of bubble inclusion is reduced.

In the discrete gas supply opening 61 example of FIGS. 10 and 11, onlyvery fine droplets (smaller than 50 μm in diameter) may be formed whenthe edge of the substrate W crosses under the fluid handling structure12. This compares with droplets up to an order of magnitude larger usinga slit gas knife. Therefore, the risk of bubble inclusion by collisionof a large droplet with the meniscus 320 is greatly reduced.

As illustrated in cross-section of FIG. 6 and in plan in FIG. 12, in anembodiment one or more grooves 220 may extend between the space betweenadjacent gas supply openings 61 and the corresponding extraction opening210 (only one is illustrated). The grooves 220 are formed on the undersurface of the fluid handling structure 12. The grooves 220 areeffective to guide liquid present in the space between the adjacent gassupply openings 61 to the corresponding extraction opening 210. Thegrooves 220 extend in a direction which passes through the space 11occupied by immersion liquid, in use.

In an embodiment the grooves extend in a direction which passes throughthe space 11 and through the corresponding extraction opening 210. In anembodiment the direction passes substantially through the center of thespace 11. During periods when the direction of relative motion betweenthe fluid handling structure 12 and the facing surface is changed, thegrooves facilitate extraction of droplets towards the extractionopenings 210. That is, if after a droplet has passed under the spacebetween adjacent gas supply openings, the relative direction of travelbetween the fluid handling structure 12 and facing surface changes, thedroplet may no longer travel in a direction relative to the fluidhandling structure 12 towards an extraction opening 210. The grooves 210help in applying a force to such droplets and thereby direct themtowards an extraction opening 210. Further details of grooves 220 aregiven in U.S. patent application publication No. US 2011-0194084.

In an embodiment each groove 220 has a width of at least 40 μm,desirably at least 50 μm. In an embodiment the groove 220 has a width ofat most 150 μm, desirably at most 100 μm. Grooves in this size range maybe particularly effective at guiding droplets and/or providing acapillary force on the droplets to pull them towards the correspondingextraction opening 210. In an embodiment, the groove 220 has a depth ofat least 50 μm, desirably at least 100 μm. In an embodiment the groovehas a depth of at most 500 μm, desirably at most 300 μm.

In an embodiment each groove has a cross-sectional shape or geometry. Agroove cross-sectional geometry may be rectangular or triangular (orV-shaped). A groove having a triangular cross-sectional shape mayexhibit enhanced capillary spreading of a liquid droplet relative agroove having a rectangular cross-sectional shape and thus may bepreferred. A triangular cross-sectional shape has a characteristic angleformed between the sides of the groove. The characteristic angle may bein the range of 40 to 45 degrees. In an embodiment, to help ensureeffectiveness of the groove in guiding liquid, the contact angle of thematerial forming the undersurface of the fluid handling structure (i.e.in which the groove is formed) has a contact angle less than thecharacteristic angle of the groove. Desirably the contact angle of thematerial is 40 degrees of less.

The grooves 220 can be used with a gas knife of a single slit opening ora plurality of gas supply openings 61 with an extraction opening 210 inthe form of a slit or in the form of a plurality of discrete openings.

A controller 500 is provided to control the flow rates and adjustment ofthe flow rates can change the pressure gradients in both the peripheral(e.g., circumferential) and tangential directions as illustrated inFIGS. 10 and 11. The flow rates and dimensions of the features of theunder surface of the fluid handling structure 12 can be adjusted toachieve the desired pressure profiles including the lowest negativepressure in the space between the gas supply openings 61 and the opening50 as illustrated in FIG. 10 as well as in helping to ensure that theminimum pressure between adjacent gas supply openings 61 (as describedabove with reference to FIG. 11) is at an acceptable level.

Very small bubbles of gas may dissolve in the immersion liquid beforethey reach the exposure area of the space 11. In an embodiment, whichcan be combined with any other embodiment, the fact that dissolutionspeed is dependent upon the type of the trapped gas and the immersionliquid properties is used.

A bubble of carbon dioxide (CO₂) typically dissolves faster than abubble of air. A bubble of CO₂ which has a solubility fifty-five (55)times larger than that of nitrogen and a diffusivity of 0.86 times thatof nitrogen will typically dissolve in a time thirty-seven (37) timesshorter than the time for a bubble of the same size of nitrogen todissolve.

U.S. patent application publication No. US 2011-0134401, herebyincorporated in its entirety by reference, describes supplying a gaswith a solubility in the immersion liquid greater than or equal to5×10⁻³ mol/kg at 20° C. and 1 atm total pressure to a region adjacentthe space 11. It also describes supplying a gas with a diffusivity inthe immersion liquid greater than or equal to 3×10⁻⁵ cm² s⁻¹ at 20° C.and 1 atm total pressure to a region adjacent the space 11. It alsodescribes supplying a gas with a product of diffusivity and solubilityin the immersion liquid of greater than that of air at 20° C. and 1 atmtotal pressure to a region adjacent the space 11.

If the bubble of gas is of a gas which has a high diffusivity,solubility or product of diffusivity and solubility in the immersionliquid, it will dissolve into the immersion liquid much faster.Therefore, using an embodiment of the invention should reduce the numberof imaging defects thereby allowing higher throughput (e.g., higherspeed of the substrate W relative to the liquid handling structure 12)and lower defectivity.

Therefore, an embodiment of the present invention provides a gassupplying device configured to supply gas to a region (e.g. to a volume,or a towards an area) adjacent the space 11. For example, gas isprovided such that it is present in the region adjacent to the meniscus320 extending between the facing surface and the liquid handlingstructure 12.

An example gas is carbon dioxide which may be desirable because it isreadily available and may be used in immersion systems for otherpurposes. Carbon dioxide has solubility in water at 20° C. and 1 atmtotal pressure of 1.69×10⁻³ kg/kg or 37×10⁻³ mol/kg. Any non-reactivegas which readily dissolves in immersion liquid is suitable.

An embodiment of the present invention herein described may form a CO₂atmosphere around the meniscus 320, 400 of immersion liquid so that anyinclusion of gas into the immersion liquid creates a gas inclusion whichdissolves in the immersion liquid.

By using gaseous CO₂ the problem associated with the meniscus collidingwith a droplet of liquid may be reduced if not alleviated. Typically adroplet of 300 micrometers would produce a bubble of 30 micrometers indiameter (i.e. a tenth the size). Such a bubble of carbon dioxide wouldusually dissolve in the immersion liquid before reaching the exposurearea. (Note that a droplet of such a size may cause one or more otherproblems). Therefore the problems caused by a droplet could be lesssignificant. The immersion system could be more tolerant of interactingwith immersion liquid which had escaped from the space.

Carbon dioxide can be provided through gas supply openings 61. In anembodiment, the gas is supplied through a second array of gas supplyopenings or through both the gas supply openings and the second array ofgas openings.

In an embodiment the flow rate of carbon dioxide out of openings 50summed with the flow rate of gas out of extraction openings 210 isgreater than or equal to the flow rate of gas out of gas supply openings61. In an embodiment, the summed gas extraction rate is more than orequal to 1.2 or desirably more than or equal to 1.4 times the gas supplyrate. For example, the gas flow rate into the openings 50 may be 60liters per minute, the gas flow rate into extraction openings 210 may be60 liters per minute and the gas flow rate out of gas supply openings 61may be 90 liters per minute. This arrangement is advantageous if the gassupplied out of the gas supply openings 61 is carbon dioxide (describedbelow). This is because carbon dioxide may interfere with aninterferometer outside the fluid handling structure 12. By arranging theflow rates as described, loss of carbon dioxide out of the fluidhandling structure 12 can be reduced or prevented.

In the case of using CO₂ in the gas knife, flow variations resultingfrom an inhomogeneity in the gas flow (such as that which appears whenusing a slit gas knife) can result in gas which is not CO₂ (e.g. air)from the atmosphere outside of the fluid handling structure 12 beingmixed into the flow which can then reach the openings 50. This can beundesirable and so there is an advantage of using a plurality of gassupply openings 61 compared to a slit.

For the case that carbon dioxide is supplied out of the gas supplyopenings 61, the distance between the extraction openings 210 and thegas supply openings 61 may be at least 1 or 2 mm or within 1.0 mm to 4.0mm, desirably within 2 mm to 3 mm. A design rule could be 4 times theworking distance plus 0.2-0.5 mm. This effectively helps prevent mixingof air from outside of the fluid handling structure 12 (i.e., airradially outwardly of the extraction openings 210) into the carbondioxide adjacent the meniscus 320.

In an embodiment, the effectiveness of extraction openings 210 inremoving liquid from a facing surface, for example in the form ofdroplets, decreases with increased distance from a threshold distancefrom the gas supply openings 61. The threshold distance for dropletremoval, for desired operating conditions, may be less than the desireddistance between the extraction openings 210 and the gas supply openings61. When using carbon dioxide as the gas exiting the gas supply openings61, it may be advantageous to use grooves 220 in the undersurface of thefluid confinement structure 12 because the grooves 220 help in extendingthe threshold distance between the gas supply openings 61 and extractionopenings 210 for droplet removal. The grooves 220 therefore assist inachieving effective carbon dioxide gas removal and droplet removalthrough the outer extractors.

The above embodiments have been described with reference to the presenceof only one linear array of gas supply openings 61 surrounding themeniscus pinning features. However, an embodiment of the presentinvention is equally applicable to the case where a second (or more)plurality of gas supply openings 61 in a linear array is positioned atleast partly to surround the first plurality of gas supply openings 61.The arrangement may be similar to that described in U.S. patentapplication publication No. US 2011-0090472 except that one or both ofthe two slit gas knifes are replaced with a plurality of discrete gassupply openings as described hereinabove. This may be advantageous whereparticularly fast relative movement between the fluid handling system 12and the facing surface occurs. Such a larger relative velocity may beused in a lithographic apparatus for exposing substrates having a largerdiameter than the current industry standard of 300 mm, for examplesubstrates of 450 mm in diameter.

In an embodiment, there is provided a fluid handling structure for alithographic apparatus, the fluid handling structure having, at aboundary of a space configured to contain immersion fluid to a regionexternal to the fluid handling structure: a meniscus pinning feature toresist passage of immersion fluid in a radially outward direction fromthe space; a plurality of gas supply openings in a linear array at leastpartly surrounding and radially outward of the meniscus pinning feature;and at least one gas recovery opening radially outward of the pluralityof gas supply openings in a linear array.

In an embodiment, the at least one gas recovery opening comprises aplurality of gas recovery openings in a linear array.

In an embodiment, there is provided a fluid handling structure for alithographic apparatus, the fluid handling structure having, at aboundary of a space configured to contain immersion fluid to a regionexternal to the fluid handling structure: a meniscus pinning feature toresist passage of immersion fluid in a radially outward direction fromthe space; an opening of a gas knife at least partly surrounding andradially outward of the meniscus pinning feature; and at least one gasrecovery opening radially outward of the opening of the gas knife, theat least one gas recovery opening comprising a plurality of gas recoveryopenings of a similar or the same size.

In an embodiment, there is provided a fluid handling structure for alithographic apparatus, the fluid handling structure having, at aboundary of a space configured to contain immersion fluid to a regionexternal to the fluid handling structure: a meniscus pinning feature toresist passage of immersion fluid in a radially outward direction fromthe space; an opening of a gas knife at least partly surrounding andradially outward of the meniscus pinning feature; and at least one gasrecovery opening radially outward of the opening of the gas knife, theat least one gas recovery opening comprising a plurality of gas recoveryopenings in a periodic pattern along a line.

In an embodiment, there is provided a fluid handling structure for alithographic apparatus, the fluid handling structure having, at aboundary of a space configured to contain immersion fluid to a regionexternal to the fluid handling structure: a meniscus pinning feature toresist passage of immersion fluid in a radially outward direction fromthe space; an opening of a gas knife at least partly surrounding andradially outward of the meniscus pinning feature; and at least one gasrecovery opening radially outward of the opening of the gas knife, theat least one gas recovery opening comprising a plurality of gas recoveryopenings equidistantly spaced apart.

In an embodiment, the opening of the gas knife comprises a plurality ofgas supply openings in a linear array. In an embodiment, each spacebetween adjacent gas supply openings of the plurality of gas supplyopenings in a linear array has a corresponding gas recovery opening ofthe plurality of gas recovery openings in a linear array. In anembodiment, the corresponding gas recovery opening is positioned suchthat a line passing through it toward a center, in plan, of the spaceconfigured to contain immersion fluid subsequently bisects thecorresponding space between adjacent gas supply openings. In anembodiment, the separation between the gas supply openings or opening ofthe gas knife and the gas recovery opening is at least 0.2 mm. In anembodiment, the separation between the gas supply openings or opening ofthe gas knife and the gas recovery opening is at most 1.0 mm. In anembodiment, the fluid handling structure further comprises a groove inan underside of the fluid handling structure extending in a directionfrom the gas supply openings or opening of the gas knife towards the gasrecovery opening. In an embodiment, the groove has a width of at least40 μm, or at least 50 μm. In an embodiment, the groove has a width of atmost 150 μm, or at most 100 μm. In an embodiment, the groove has a depthof at least 50 μm. In an embodiment, the groove has a depth of at most500 μm. In an embodiment, the meniscus pinning feature comprises aplurality of openings in a linear array. In an embodiment, the meniscuspinning feature comprises a single phase extractor. In an embodiment,the gas supply openings or opening of the gas knife has, in plan, acornered shape.

In an embodiment, there is provided an immersion lithographic apparatus,the apparatus comprising: the fluid handling structure as describedherein.

In an embodiment, there is provided a device manufacturing method,comprising: projecting a patterned beam of radiation through animmersion liquid confined to a space between a projection system and asubstrate; providing gas through a plurality of gas supply openings in alinear array to a position adjacent a meniscus of the immersion liquid;and recovering liquid which passes through adjacent gas supply openingsof the plurality of gas supply openings in a linear array through a gasrecovery opening radially outward of the plurality of gas supplyopenings in a linear array.

In an embodiment, there is provided a device manufacturing method,comprising: projecting a patterned beam of radiation through animmersion liquid confined to a space between a projection system and asubstrate; providing gas through an opening of a gas knife to a positionadjacent a meniscus of the immersion liquid; and recovering liquid whichpasses the opening of the gas knife through at least one gas recoveryopening radially outward of the opening of the gas knife, the at leastone gas recovery opening comprising a plurality of gas recovery openingsof a similar or the same size.

In an embodiment, there is provided a device manufacturing method,comprising: projecting a patterned beam of radiation through animmersion liquid confined to a space between a projection system and asubstrate; providing gas through an opening of a gas knife to a positionadjacent a meniscus of the immersion liquid; and recovering liquid whichpasses the opening of the gas knife through at least one gas recoveryopening radially outward of the opening of the gas knife, the at leastone gas recovery opening comprising a plurality of gas recovery openingsin a periodic pattern along a line.

In an embodiment, there is provided a device manufacturing method,comprising: projecting a patterned beam of radiation through animmersion liquid confined to a space between a projection system and asubstrate; providing gas through an opening of a gas knife to a positionadjacent a meniscus of the immersion liquid; and recovering liquid whichpasses the opening of the gas knife through at least one gas recoveryopening radially outward of the opening of the gas knife, the at leastone gas recovery opening comprising a plurality of gas recovery openingsequidistantly spaced apart.

As will be appreciated, any of the above described features can be usedwith any other feature and it is not only those combinations explicitlydescribed which are covered in this application. For example, anembodiment of the invention could be applied to the embodiments of FIGS.2 to 4.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 248, 193, 157 or 126 nm). The term“lens”, where the context allows, may refer to any one or combination ofvarious types of optical components, including refractive and reflectiveoptical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, the embodiments of the invention maytake the form of a computer program containing one or more sequences ofmachine-readable instructions describing a method as disclosed above, ora data storage medium (e.g. semiconductor memory, magnetic or opticaldisk) having such a computer program stored therein. Further, themachine readable instruction may be embodied in two or more computerprograms. The two or more computer programs may be stored on one or moredifferent memories and/or data storage media.

Any controllers described herein may each or in combination be operablewhen the one or more computer programs are read by one or more computerprocessors located within at least one component of the lithographicapparatus. The controllers may each or in combination have any suitableconfiguration for receiving, processing, and sending signals. One ormore processors are configured to communicate with the at least one ofthe controllers. For example, each controller may include one or moreprocessors for executing the computer programs that includemachine-readable instructions for the methods described above. Thecontrollers may include data storage medium for storing such computerprograms, and/or hardware to receive such medium. So the controller(s)may operate according the machine readable instructions of one or morecomputer programs.

One or more embodiments of the invention may be applied to any immersionlithography apparatus, in particular, but not exclusively, those typesmentioned above and whether the immersion liquid is provided in the formof a bath, only on a localized surface area of the substrate, or isunconfined. In an unconfined arrangement, the immersion liquid may flowover the surface of the substrate and/or substrate table so thatsubstantially the entire uncovered surface of the substrate table and/orsubstrate is wetted. In such an unconfined immersion system, the liquidsupply system may not confine the immersion liquid or it may provide aproportion of immersion liquid confinement, but not substantiallycomplete confinement of the immersion liquid.

A liquid supply system as contemplated herein should be broadlyconstrued. In certain embodiments, it may be a mechanism or combinationof structures that provides a liquid to a space between the projectionsystem and the substrate and/or substrate table. It may comprise acombination of one or more structures, one or more fluid openingsincluding one or more liquid openings, one or more gas openings or oneor more openings for two phase flow. The openings may each be an inletinto the immersion space (or an outlet from a fluid handling structure)or an outlet out of the immersion space (or an inlet into the fluidhandling structure). In an embodiment, a surface of the space may be aportion of the substrate and/or substrate table, or a surface of thespace may completely cover a surface of the substrate and/or substratetable, or the space may envelop the substrate and/or substrate table.The liquid supply system may optionally further include one or moreelements to control the position, quantity, quality, shape, flow rate orany other features of the liquid.

In an embodiment, the lithographic apparatus is a multi-stage apparatuscomprising two or more tables located at the exposure side of theprojection system, each table comprising and/or holding one or moreobjects. In an embodiment, one or more of the tables may hold aradiation-sensitive substrate. In an embodiment, one or more of thetables may hold a sensor to measure radiation from the projectionsystem. In an embodiment, the multi-stage apparatus comprises a firsttable configured to hold a radiation-sensitive substrate (i.e., asubstrate table) and a second table not configured to hold aradiation-sensitive substrate (referred to hereinafter generally, andwithout limitation, as a measurement and/or cleaning table). The secondtable may comprise and/or may hold one or more objects, other than aradiation-sensitive substrate. Such one or more objects may include oneor more selected from the following: a sensor to measure radiation fromthe projection system, one or more alignment marks, and/or a cleaningdevice (to clean, e.g., the liquid confinement structure).

In an embodiment, the lithographic apparatus may comprise an encodersystem to measure the position, velocity, etc. of a component of theapparatus. In an embodiment, the component comprises a substrate table.In an embodiment, the component comprises a measurement and/or cleaningtable. The encoder system may be in addition to or an alternative to theinterferometer system described herein for the tables. The encodersystem comprises a sensor, transducer or read-head associated, e.g.,paired, with a scale or grid. In an embodiment, the movable component(e.g., the substrate table and/or the measurement and/or cleaning table)has one or more scales or grids and a frame of the lithographicapparatus with respect to which the component moves has one or more ofsensors, transducers or read-heads. The one or more of sensors,transducers or read-heads cooperate with the scale(s) or grid(s) todetermine the position, velocity, etc. of the component. In anembodiment, a frame of the lithographic apparatus with respect to whicha component moves has one or more scales or grids and the movablecomponent (e.g., the substrate table and/or the measurement and/orcleaning table) has one or more of sensors, transducers or read-headsthat cooperate with the scale(s) or grid(s) to determine the position,velocity, etc. of the component.

In an embodiment, the lithographic apparatus comprises a liquidconfinement structure that has a liquid removal device having an inletcovered with a mesh or similar porous material. The mesh or similarporous material provides a two-dimensional array of holes contacting theimmersion liquid in a space between the final element of the projectionsystem and a movable table (e.g., the substrate table). In anembodiment, the mesh or similar porous material comprises a honeycomb orother polygonal mesh. In an embodiment, the mesh or similar porousmaterial comprises a metal mesh. In an embodiment, the mesh or similarporous material extends all the way around the image field of theprojection system of the lithographic apparatus. In an embodiment, themesh or similar porous material is located on a bottom surface of theliquid confinement structure and has a surface facing towards the table.In an embodiment, the mesh or similar porous material has at least aportion of its bottom surface generally parallel with a top surface ofthe table.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

The invention claimed is:
 1. A fluid handling structure for alithographic apparatus, the fluid handling structure configured toconfine immersion fluid to a space, the fluid handling structurecomprising: a meniscus pinning feature to resist passage of immersionfluid in a radially outward direction from the space; a plurality of gassupply openings in a linear array at least partly surrounding andoutward, relative to the space, of the meniscus pinning feature; and aplurality of gas recovery openings in a linear array outward, relativeto the space, of the plurality of gas supply openings in a linear array,wherein each space between adjacent gas supply openings of the pluralityof gas supply openings in a linear array has a corresponding gasrecovery opening of the plurality of gas recovery openings in a lineararray, and each space between adjacent gas recovery openings has acorresponding gas supply opening such that the corresponding gas supplyopening is positioned directly radially inward of each respective spacebetween adjacent gas recovery openings.
 2. The fluid handling structureof claim 1, wherein the plurality of gas recovery openings are of asimilar or the same size.
 3. The fluid handling structure of claim 1,wherein the plurality of gas recovery openings are in a periodic patternalong a line.
 4. The fluid handling structure of claim 1, wherein theplurality of gas recovery openings are equidistantly spaced apart. 5.The fluid handling structure of claim 1, wherein the separation betweenthe gas supply openings and the gas recovery openings is at least 0.2mm.
 6. The fluid handling structure of claim 1, wherein the separationbetween the gas supply openings and the gas recovery openings is at most1.0 mm.
 7. The fluid handling structure of claim 1, further comprising agroove in an underside of the fluid handling structure extending, andbeing elongate, in a direction from the gas supply openings towards thegas recovery openings.
 8. The fluid handling structure of claim 7,wherein the groove has a width of at least 40 μm.
 9. The fluid handlingstructure of claim 7, wherein the groove has a width of at most 150 μm.10. The fluid handling structure of claim 7, wherein the groove has adepth of at least 50 μm.
 11. The fluid handling structure of claim 7,wherein the groove has a depth of at most 500 μm.
 12. The fluid handlingstructure of claim 1, wherein the meniscus pinning feature comprises aplurality of openings in a linear array.
 13. The fluid handlingstructure of claim 1, wherein the meniscus pinning feature comprises asingle phase extractor.
 14. The fluid handling structure claim 1,wherein the gas supply openings has, in plan, a cornered shape.
 15. Alithographic apparatus, comprising: a substrate table configured to holda substrate; a projection system configured to project a patterned beamon the substrate; and a fluid handling structure configured to confineimmersion fluid to a space between the projection system and thesubstrate table, the fluid handling structure comprising: a meniscuspinning feature to resist passage of immersion fluid in a radiallyoutward direction from the space, a plurality of gas supply openings ina linear array at least partly surrounding and outward, relative to thespace, of the meniscus pinning feature, and a plurality of gas recoveryopenings in a linear array outward, relative to the space, of theplurality of gas supply openings in a linear array, wherein each spacebetween adjacent gas supply openings of the plurality of gas supplyopenings in a linear array has a corresponding gas recovery opening ofthe plurality of gas recovery openings in a linear array, and each spacebetween adjacent gas recovery openings has a corresponding gas supplyopening such that the corresponding gas supply opening is positioneddirectly radially inward of each respective space between adjacent gasrecovery openings.
 16. The lithographic apparatus of claim 15, furthercomprising a groove in an underside of the fluid handling structureextending, and being elongate, in a direction from the gas supplyopenings towards the gas recovery openings.
 17. The lithographicapparatus of claim 15, wherein the separation between the gas supplyopenings and the gas recovery openings is at most 1.0 mm.
 18. Thelithographic apparatus of claim 15, wherein the meniscus pinning featurecomprises a plurality of openings in an array.
 19. A devicemanufacturing method, comprising: projecting a patterned beam ofradiation through an immersion liquid confined to a space between aprojection system and a substrate; providing gas through a plurality ofgas supply openings in a linear array to a position adjacent a meniscusof the immersion liquid; and recovering liquid which passes throughadjacent gas supply openings of the plurality of gas supply openings ina linear array through a plurality of gas recovery openings in a lineararray radially outward of the plurality of gas supply openings in alinear array, wherein each space between adjacent gas supply openings ofthe plurality of gas supply openings in a linear array has acorresponding gas recovery opening of the plurality of gas recoveryopenings in a linear array, and each space between adjacent gas recoveryopenings has a corresponding gas supply opening such that thecorresponding gas supply opening is positioned directly radially inwardof each respective space between adjacent gas recovery openings.
 20. Themethod of claim 19, wherein the plurality of gas recovery openings areof a similar or the same size and arranged in a periodic pattern along aline.